Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $45.41   7.777%   $48.9415   $48.94   $48.95   $48.90  
  Purchase #2 $102.85   13.139%   $116.3635   $116.36   $116.35   $116.40  
  Purchase #3 $187.25   7.497%   $201.2881   $201.29   $201.30   $201.30  
  Purchase #4 $232.26   6.313%   $246.9226   $246.92   $246.90   $246.90  
  Purchase #5 $159.40   12.783%   $179.7761   $179.78   $179.80   $179.80  
  Purchase #6 $213.85   9.302%   $233.7423   $233.74   $233.75   $233.70  
  Purchase #7 $181.29   6.459%   $192.9995   $193.00   $193.00   $193.00  
  7 purchase totals = $1,122.31       $1,220.0336   $1,220.03   $1,220.05   $1,220.00